This invention relates to vascular repair devices, and in particular intravascular stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery, to maintain the patency thereof. Stents are particularly useful in the treatment of atherosclerotic stenosis in arteries and blood vessels. More particularly, the invention concerns a tapered drug-eluting stent delivery system consisting of an intravascular device having a local drug-eluting component that is capable of eluting therapeutic drugs with uniform and controlled drug distribution at a treatment site while covering at least a portion of, or all of, a balloon shoulder or taper region such that when deployed the stent extends to the point in the arterial wall where the artery is at reference vessel size.
Intravascular interventional devices such as stents are typically implanted within a vessel in a contracted state, and expanded when in place in the vessel in order to maintain the patency of the vessel to allow fluid flow through the vessel. Stents have a support structure such as a metallic structure to provide the strength required to maintain the patency of the vessel in which it is to be implanted, and are often provided with an exterior surface coating to provide a biocompatible and/or hemocompatible surface. Since it is often useful to provide localized therapeutic pharmacological treatment of a blood vessel at the location being treated with the stent, it is also desirable to provide intravascular interventional devices such as stents with a biocompatible and/or hemocompatible surface coating of a polymeric material with the capability of being loaded with therapeutic agents, to function together with the intravascular devices for placement and release of the therapeutic drugs at a specific intravascular site.
Drug-eluting stent devices have shown great promise in treating coronary artery disease, specifically in terms of reopening and restoring blood flow in arteries stenosed by atherosclerosis. Restenosis rates after using drug-eluting stents during percutaneous intervention are significantly lower compared to bare metal stenting and balloon angioplasty. However, it appears that another phenomena which limits the performance of drug-eluting stent devices has emerged. Recent studies have indicated that the commonly called “candy-wrapper” effect is genuine in drug-eluting stent devices and is a definite limiting factor in their performance. The term “candy-wrapper” effect refers to the occurrence of in-segment or edge restenosis in a vessel treated by intravascular intervention. “Candy-wrapper” ends may result from a non-uniform drug dose at the ends of the stent and/or excessive vessel injury at the stent margins and in the shoulder region. The “candy-wrapper” effect typically starts at the proximal and distal edges of a treatment region and extends outward about 3 mm to 5 mm or more. Several potential reasons for this effect, many of which were first articulated in response to the candy wrapper effects seen with radioactive stents, include the following: (1) balloon injury outside of the stented area; (2) a stimulatory effect on the tissues by the active agent at the lower concentrations outside of the stent; (3) geographic miss during stent placement which implies the stenosis was somewhat there to begin with; and (4) an especially large amount of vessel injury at the stent edge itself as that is a point of maximum wall stress. Of the aforementioned reasons, the first and fourth reasons are the most plausible. Accordingly, if such reasons are true, edge restenosis occurs because the drug tissue concentration falls off rapidly outside of the stent.
What has been needed and heretofore unavailable in the art is a drug-eluting stent delivery system that would be effective in the treatment of edge restenosis within the reference vessel. By minimizing vessel injury outside the stented section of the vessel, the occurrence of edge effects will likely be reduced. Thus, it would be desirable to have a drug-eluting stent that is optimally designed to have tapered end portions so that the region of drug treatment would be extended into the stent shoulder regions of the vessel. The present invention meets these and other needs.